Add functions stub for compatibility with very minimal libc

[facchinm]

In case the user needs to call the functions from Print/String, these placeholders should be implemented (with C++ scope)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (5b9faf6) 95.77% compared to head (e1d6500) 95.77%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #188   +/-   ##
=======================================
  Coverage   95.77%   95.77%           
=======================================
  Files          13       13           
  Lines         970      970           
=======================================
  Hits          929      929           
  Misses         41       41           

Impacted Files	Coverage Δ
api/Print.cpp	95.20% <ø> (ø)
api/String.cpp	97.65% <ø> (ø)

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